Project Summary/Abstract ? Project 4 Radiation Pneumonitis/Fibrosis There is a critical, unmet need to develop medical countermeasures (MCM) for the mitigation of the delayed effects of acute radiation exposure (DEARE), namely radiation pneumonitis/fibrosis, in victims successfully treated for acute radiation sickness following a radiological or nuclear incident. The overall objective of project 4 is to complete activities necessary to bring BIO 300 (?BIO 300?) nanosuspension (Humanetics Corporation, Edina, MN) towards approval under the U.S. Food and Drug Administration (FDA) Animal Rule regulatory pathway for the indication to increase survival in individuals acutely exposed to pulmonary-toxic doses of radiation [e.g. delayed effects of acute radiation-exposure (DEARE)-lung]. Our published data indicates BIO 300 (400 mg/kg, QD, oral gavage) confers a significant improvement in survival from DEARE-lung when treatment is started 24 hours after exposure to life-threatening doses of radiation and continued for six weeks (5). Further, clinical data demonstrate an excellent safety profile when BIO 300 is administered as a daily oral regimen (500 - 1500 mg) over a minimum duration of six weeks. Project 4 is highly interactive with the other Projects and Cores within the INTERACT Consortium. Studies in Aim 1 are designed to optimize the BIO 300 dosing regimen to maximize the likelihood of survival from DEARE- lung. Higher drug exposure has been observed in murine and non-human primate models when BIO 300 is administered by intramuscular (IM) injection versus oral administration. Therefore, IM administration may further improve the therapeutic benefit of BIO 300 on 220-day survival and mitigation of lung damage beyond that observed with oral dosing. Specific Aim 2 will be conducted in collaboration with Core B-Multispecies Efficacy and Pharmacometric Modeling. Experiments in this aim are designed to identify and validate plasma-based pharmacodynamic (PD) biomarkers associated with BIO 300 mediated ERb activation and downstream effects on cellular senescence in rodents and NHP. A systems biology approach incorporating pharmacometric modeling will be utilized, and will incorporate known BIO 300-mediated effects on PD biomarkers in cancer patients undergoing clinical radiation therapy to relate the proposed mechanism of action of BIO 300 in animal models to the presumed mechanism in humans. The role of cellular senescence in DEARE-lung is further explored in Aim 3 through the testing of senolytic agents alone or in combination with BIO 300. Further, Aim 3 will address knowledge gaps relevant to the pathophysiological mechanisms underlying ARS evolving towards DEARE and testing of novel senolytic agents (BCL-xL-P) through strong collaborations with Projects 1, 2, and 3. Power calculations and statistical analysis for Project 4 will be performed by the biostatistician in Core A - Administrative Core. The proposed Aims are only achievable through a cooperative research agreement, as proposed by the INTERACT Consortium, whose members bring together expertise in every major area required to probe the complex biological processes orchestrating radiation damage in lung tissue and discover new biomarkers for tissue injury and recovery.